How to apply strain rate a tensile Test
Doğan ACAR
l...@schwer.net
The easiest way to prescribe strain rate is using prescribed velocity.
Strain = displacement / length
Strain rate = strain / time = displacement / (length * time) = velocity / length
Where length is the length of your tensile specimen.
This will provide an approximate strain rate – as the length of the specimen changes under deformation the resulting strain rate will decrease.
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Doğan ACAR
James M. Kennedy
Dear Dogan,
In general, if you increase the velocity of the moving end of the specimen, you can hope to
decrease the termination time needed to capture the primary response of the test specimen.
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Anders Jernberg of ERAB provided this very nice presentation regarding termination time
and the possible role of mass scaling:
The first rule is that you wish to set it to as low as possible to reduce simulation time. There
are basically two reasons for why the termination become a certain value.
(1) You might want to simulate some short (in time) physical phenomena where dynamic
effects are essential for the behavior, like car crash, hitting a golf ball or whatever. Here you
have to estimate for how long you need to perform the simulation to catch the behavior you
wish to analyze. That estimation sets the termination time.
(2) You wish to perform an analysis where you don't want the inertia effects to affect the
results, like applying a static load to a structure. Running the explicit solver and applying the
load too fast you will get inertia effects that changes the structural response. Applying a load
very fast, and it finally becomes more like an impact simulation. I believe the best way to apply
a load for (explicit) static analysis is to ramp it up to the final load using a half sine function
shape for the load. The duration for the ramp-up time to get reasonable small kinetic energy
compared to internal energy correlates to the eigenfrequency of the system. A minimum reason-
able ramp-up time for quasi static analysis is 1.5-2.0 times the normal period (1./frequency) of
the system. That sets the termination time in this case.
You can reduce the CPU time by specifying mass scaling. For quasi-static analysis, I believe
selective mass scaling is superior. It will not let you set shorter termination time but the time
step can be larger.
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Sincerely,
James M. Kennedy
KBS2 Inc.
March 12, 2022
From: ls-d...@googlegroups.com [mailto:ls-d...@googlegroups.com] On Behalf Of Dogan ACAR
Sent: Wednesday, March 09, 2022 5:28 AM
To: LS-DYNA2 <ls-d...@googlegroups.com>
Subject: [LS-DYNA2] How to apply strain rate a tensile Test
Dear all,
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